1. Field of the Invention
The present invention relates to semiconductor processing and, in particular, concerns a metalorganic chemical vapor deposition (MOCVD) technique for forming component layers, such as platinum layers, in a manner that results in more efficient deposition of the component layer onto the surface of a semiconductor device.
2. Description of the Related Art
Semiconductor processing techniques have become increasingly more complex as a result of the increasing density and smaller sizes of semiconductor devices. One particular problem that occurs with smaller sized semiconductor devices is that it is often difficult to form components, such as conductors, vias and electrodes, that conformally cover the contours of the semiconductor device. For example, a typical device formed by semiconductor processing is a capacitor. Typically, a capacitor is formed in an opening in an isolation layer of a semiconductor device and has two electrodes that are positioned within the opening with a dielectric separating the electrodes so as to cover both the side walls and the bottom floor of the opening. It will be appreciated that as the openings become smaller and smaller in size, it is increasingly more difficult to have the electrode formed so as to uniformly cover the side walls and bottom walls of the opening. Three dimensional capacitors are but one example of a device that is increasingly more difficult to fabricate due to decreasing device dimensions leading to difficulties with conformal covering of the device surface. Other devices in which this problem occurs include vias, electrodes and conductive lines.
To address the particular problems associated with forming electrodes and other conductive elements on 3-dimensional surfaces, various techniques using various materials have been developed. One particularly common technique for forming three dimensional conductive elements, vias and lines in semiconductor applications is to use Chemical Vapor Deposition (CVD) techniques to deposit a conductive material, such as platinum (Pt), within an opening formed to contain a 3-dimensional conductive element.
For example, platinum is viewed as an ideal electrode material for high-K capacitors in DRAM applications due to its relatively high work function. This high work function forms an increased energy barrier inhibiting leakage migration of charge carriers between electrodes through an intervening dielectric. Moreover, platinum is also generally not oxidizable such that the electrode""s resistivity is not increased as a result of exposure to oxygen containing compounds contained within the semiconductor environment.
Further, platinum is also strongly favored for formation of electrodes and 3-dimensional semiconductor structures, such as capacitors, conductors, vias and the like, due to its particularly advantageous step coverage when applied using chemical vapor deposition (CVD) techniques. In particular, platinum can be used to coat 3-dimensional structures through chemical vapor deposition such that the vertical side walls and the horizontal bottom surfaces are adequately covered by the deposited platinum.
Typically, a platinum precursor and other reactants are introduced into the CVD chamber and the platinum carried by a precursor gas is then deposited onto the surface of the semiconductor substrate through thermal decomposition or reaction with another reactant gas, such as O2, N2O, or H2. The platinum is carried in the precursor gas, that often comprises an organic compound. The platinum atom is bonded to the organic compound to permit the platinum atoms to be transferred in the gas phase. This enables the Pt to be conformally deposited over the surface of the wafer as the organic compound facilitates improved step coverage.
In the prior art, there is generally only a single deposition step such that the precursor gas and other reactant gas(es) are flowed into the CVD chamber until enough platinum, carried by the precursor gas, has been deposited on the exposed surface to form an electrode or other conductive element of a desired thickness. However, current CVD platinum deposition techniques have particularly low deposition efficiency such that the deposition rate is very slow, on the order of 1 Angstrom per second. In order to obtain a 300 Angstrom film, the deposition time is therefore usually several minutes. The relatively slow deposition rate creates inefficiencies in the manufacturing of semiconductor devices.
Moreover, the platinum precursor gas used for deposition is particularly expensive, on the order of $100 per gram. It has been observed that typical CVD platinum deposition techniques result in enormous waste of this expensive platinum precursor gas as only a small proportion of the platinum carried by the precursor gas is actually being deposited on the semiconductor wafer positioned in the CVD chamber. Hence, not only are current CVD platinum deposition techniques slow, they are also particularly inefficient in delivering platinum to the wafer. This results in considerable waste of expensive material and increases the cost of manufacturing semiconductor devices that require 3-dimensional conductive structures, like electrodes or conductors.
Further, the deposition process also results in the possible deposition of hydrocarbon byproducts on the surface of the semiconductor device which can become incorporated into or adsorbed onto the surface of the deposited film contaminating the film and inhibiting further deposition. In particular, the deposition of platinum in one typical process proceeds by the formula:
(C5H5)Pt(CH3)3+H2xe2x86x92Pt (film)+CH4+ other hydrocarbons
The other hydrocarbons may not be volatile enough at the deposition temperature and thus stay on the surface of the film following deposition. This can result in contamination of the film and inhibit further deposition of the platinum film.
From the foregoing, it will be appreciated that there is a need for an improved technique for depositing conductive materials onto a semiconductor surface such that good step coverage can be obtained without a significant increase in the cost of manufacturing the semiconductor device. To this end, there is a need for a more efficient way of depositing conductive material, such as platinum, in a manner that results in more efficient deposition of the material with less waste of the precursor material used to form the material.
The aforementioned needs are satisfied by the present invention which, in one aspect, comprises a method of forming a conductive layer comprising (a) positioning a semiconductor device within a CVD chamber, (b) exposing the semiconductor device to a precursor gas containing a conductive element and a reactant to form the conductive layer for a first period of time, (c) exposing the semiconductor substrate to a reactant so that the reactant reacts with organic compounds contained within the conductive layer, and (d) reintroducing the precursor gas into the CVD chamber following exposure of the semiconductor substrate to the reactant so as to further form the conductive layer on the semiconductor device.
In one particular embodiment, a semiconductor device with a defined opening for a 3-dimensional capacitor is positioned within a CVD chamber and is exposed to a precursor gas containing platinum which is then deposited using chemical vapor deposition techniques. A reactant is also introduced into the CVD chamber wherein the deposited platinum material is exposed to the reactant. The reactant can comprise any of a number of elements, compounds or processes, such as, for example, the introduction of a gas such as H2, N2O, NO, H2O, O2, ozone, or some other oxygen containing ambient, into the CVD chamber or with the enhancement of plasma or UV light. Moreover, the conductor can comprise not only platinum, but also other conductive films such as Ir, Rh, Ni, Co, Cu, W, and the like.
In one embodiment, the reactant gas is introduced at the same time as the conductive precursor gas. In another embodiment, the reactant gas is introduced following the introduction of the precursor gas for a selected period of time. In either circumstance, the reactant gas reacts with the residual organic compounds so as to remove the residual organic compounds in or on the surface of the deposited films thereby increasing the deposition efficiency.
Organic by-products can be adhered to the exposed surface of the deposited conductive layer. By introducing a reactant into the CVD chamber, the organic compounds can be removed by reaction with the reactants thereby making available more conductor nucleating sites and allowing greater absorption of the conductor precursor in the vapor phase.
In another aspect of the invention, a system for forming a conductive layer on a semiconductor device is provided. In this aspect, the system includes a CVD chamber which receives the semiconductor device; a metal organic precursor gas source which provides a metal organic precursor gas with entrained conductive particles; a reactant source that provides a reactant to the CVD chamber and a controller which controls the delivery of conductive precursor gas and reactant into the CVD chamber. In this aspect, the controller allows for the delivery of the conductive precursor gas and the reactant into the chamber. The reactant is selected to react with organic compounds of the conductive precursor gas so as to remove the organic compound from the formed conductive layer. Hence, by delivering both the precursor and the reactant, either simultaneously or sequentially or both, the efficiency of the deposition process can be improved.
In one particular embodiment, the system includes a sensor, such as, for example, a mass spectrometer, that provides a signal to the controller indicative of the deposition of the conductive precursor gas by the semiconductor device. When the deposition drops below a particular threshold, such that there is increased waste of the conductive precursor gas, the controller then induces the delivery of the reactant into the chamber.